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1.
When your brain attacks itself (one realizes this on a conscious level). One might feel as if they are "going crazy".
In conversation involving size comparison of two rivalving penis sizes....one man considers his size inferior to rivals, and asks odd request best male freind:

"Will you please listen to me, I'm creating mentacide....will you please check out my size and tell me if it's normal or not? Hemingway did it for Fitzgerald!"
by fabcat March 09, 2012